Carbon type microphone



Sept. 27, 1949. c. LAURENT CARBON TYPE MICROPHONE Filed Jan. 7, 1946 Patented Sept. 27, 1949 fiazisasii -CARBQNLJLYPE MmRoPHoNE ihailesi'LaurentfTarisFrance LSection12511lib'lie"Law 690, August 8, 1946 .Ii-'Tatentxpires January-12731964 c.JI-the Ninvention. has fior .itsfpbject vvarious neims prnvements in a .microphone diaphragmcasaand emoregespecially-- toman improvementi of: its Yetelesphonic qualities, mainlyfithe clearness.as alsona simplicationof itswmanufacture.

To rthiseiect,z the new:V casezfaccording to the invention comprises. thegvarious :special-Y features .as follows da) ,Thegranuler chamber isdisposed `inesuch .a wayathat :accidental :decentering `b etween thepart of this`chamber united to the movable electrode andifthat; joined"r to.- .the-'stationary electrode shall have no influence upon the settling of the carbon powder in thischamber.

(b) The material utilized for this granule `-chamb'erfand particularly' for'its hollowgpa'rt, can be given a near perfect polislfinordertoreduce the friction ofrthe .carbon .powder between the electrodes,`friction being the source of detrimental vibrations. Without being@ restricted ftoff-Itheir especi'c use, thefollowing materials may'lbe" use'd: .icellulese':acetate, porcelain, glass/,teta y cfci The reanpartofthisignanular chamber has :.aaishapede'signedto.prevent settling of thergraphtite;L powder. Y

1 1'; Cd) T1 The-:granularmchamber isl 5cl osedi byumeans co'ftwo. superposed...supple`diaphragms made Cof a sli'ght'fabric suchash forexamplef silk, cotton'ilraycon, etcif; the thin lower di aphragm being i rough sand the-upper` oneimperviouslztoimoisture.

(e) The electrodes have a shape designed particularly to provide ahigheiiiciency and to partially aid the eiiiciency of the microphoneattained xbytthe orientation oflthefseeker. Thisz-lshape is characterized by a 'iiatpportioncomprisingacentral arc.

(f) The general dimensioning permits of obtaining the desired resistance (50 ohm) without any burning out.

(g) A special part allows the adaptation of the mechanical impedance of the granular chamber and of that of the microphone diaphragm, so that the microphone Will be at the same time, both, direct acting (agitation of the granules by the electrode) and indirect acting, (agitation of the granules by means of an agitator that, in fact, is constituted by the part of the diaphragm made of rough silk in the adapter plate).

(h) The part that is required in most microphones to lead in the current to the movable electrode independently of the diaphragm is made with a View to modifying, by its elasticity, the characteristics of the utilized usual type vibrating diaphragm, and, more particularly, its output at the high frequencies by modication of the vibrating system formed `byithewholerofctlfiendiafphragm; speciaifspringg:themovable,electrodefand itsia'd listings-nut. Y

(i) A special, slightlyelastical part-enables the 5 :assembly .ofe the# wholeitoebesecuredffby afsingle lg'niniacrfsetting,without ther-necessityi-of any: me-

chanical means that wouldfbefdifiicultztoarrange onithecase.

. f (.y ),rA sspecial' mssembiyfailows- ,fofrattainingfat l the same-,timenfastening mhtheidiaphragmf-upon the movable electrode, obturailngwof-fthe chamber,

securing. of '.thescited- :adapten-f gfsandfiof the ssprfingtimh, by meanseof afsinglennutrtherebyfre- -`dueigng theinertiaofcthe whole.

i Ther -follcwingfl description?. @f-naspreferredeem- Aebodiment off-the mieniphoneediinzihragmxy caseras i illustrated in ,thaac ccmpa-nying ldfrawings ,-issgi-ven fmerelyeby-.wayofexampleandfwithoutabeingviimitative. Y, Y In vthe- :drawings ,-xlilig;A Il. is wafsectional .viewy fof armicrmihonef,l diaphragmfcase construe-ted#in` accordancefwithe the .,.presentcinventiom used-ini. theecase.

As shown in the drawings, the case comprises-a x'lxolflsingrk f-I IJ containing the-:entire `eunit fsecured tif' -ftherein byfafgjoint lltby rr-neans-cf'va conicahring .alzandthei edge. M of thewprotectinggratei,

The lvilesati-ng::diaphragms-I 5 isi lheld be tween theedgeAM and ria:s'Feciallyfsliaped metallic elemente-,2 (l having:asthmasl-ightlyvelastic part-f2 l andaaiheelaportion f.22=l contacting fthewextremity offthenxedpartsoithe granuleochamber which, itself, is inherent in the housing I0. l

The granule chamber 30 is connected to th housing l0 by being gripped betwen the stationary electrode 40 and the electrode support 4| by means of an insulating plate 38. The obturation of the granule chamber 3U is obtained by the diaphragm 3l formed of two superposed layers of silk, the lower layer 3Ib being rough and the upper one 3Ia impervious to moisture. This diaphragm is gripped between the heel 22 of the element 20 and the upper border 32 of the granule chamber, by means of the circular edge 33a of the part 33 forming a spring and being used to establish the connection between the front electrode and the housing I0 by means of the metallic element 20.

The spring 33, as more clearly shown in Fig. 3, is designed so as to modify by its elasticity the characteristics of the vibratory system formed by 3 the diaphragm I5, electrode 45, adjusting nut 46, and, in an auxiliary way, the elastic part 2| and the several air chambers. 'I'his modification has for its object an improvement of the high frequency transmission.

The inner face 35 of the granule chamber 30, made of a suitable material, is carefully polished so as to prevent all parasitic vibrations. The granule reservoir, formed by the cavity 36 in the granule chamber, is designed to avoid settling. The electrodes 40 and 45 are made of either carbon and brass or a gilded brass. The meridian of these planes presents straight parts 42, 41 and circular parts 43, 48. Because of the two circular parts, the granule chamber presents the shape of a spherical cap 31.

Decentering of the axis of the electrode 45 with respect to the electrode 40 is absorbed by the play of the heel 22 due to the flexibility of the elastic part 2 I without causing any parasitic deformation of the granule chamber.

A steel disc 34 allows the coaction between the mechanical impedance of the diaphragm and that of the granule chamber.

This disc supports a circular portion 33 of the part 33 by which it is caused to bear upon the edge 4l of the electrode 45.

Finally, the drawing shows clearly how a single nut 46 maintains the diaphrgam l5, spring 33, adapter 34, diaphragm 3| and electrode 45.

What is claimed is:

1. In a microphone diaphragm case, a granule chamber, a stationary electrode in said granule chamber comprising a central concave portion and a surrounding straight portion of substantial width, a vibrating diaphragm, a movable electrode connected to said vibrating diaphragm, said movable electrode comprising a central convex portion and a surrounding straight portion of substantial width, said electrodes partially defining said granule chamber and forming a central spherical cup portion therein and a plane portion surrounding said cup portion, said chamber having an anular portion surrounding said plane portion, a circular spring member carryingY said movable electrode, a rim maintaining the edge of said circular member and a flexible element united to said rim. f

2. In a microphone diaphragm case as claimed in claim 1, an annular plate interposed between said movable electrode and said circular member for adjusting the mechanical impedance of the said granule chamber with respect to said microphone diaphragm, said circular member having a projection thereon for maintaining contact between said annular plate and said movable electrode.

Lil)

3. In a microphone diaphragm case as claimed in claim 2, a. diaphragm between said movable electrode and said annular plate closing said granule chamber, said diaphragm comprising two thin superposed supple diaphragms of light fabric, the lower of said diaphragms being rough and the upper of said diaphragms being impervious to moisture, said diaphragm providing obturation in said granule chamber.

`4. In a microphone capsule, a casing, a vibrating diaphragm carried by said casing, a movable electrode integral with said diaphragm, a fixed electrode secured within said casing, a granule chamber between said two electrodes, the latter being so shaped as to provide therebetween a concave interval surrounded by a straight interval, a cup-shaped member of insulating material in the casing bottom, said cup-shaped member having an annular recess for the granules surrounding said straight interval.

5. In a microphone capsule, a casing, a vibrating diaphragm carried by said casing, a movable electrode integral with said diaphragm, a fixed electrode secured within said casing, a granule chamber between said two electrodes, the latter being so shaped as to provide therebetween a concave interval surrounded by a straight interval, a cup-shaped member of insulating material in the casing bottom, said cup-shaped member having an anular recess with a perfectly polished surface.

CHARLES LAURENT.

REFERENCES CITED The following references are of record in the file of this patenti UNITED STATES PATENTS Number Name Date 518,263 Milde Apr. 17, 1894 678,972 Nolen July 23, 1901 '718,310 Cadden Jan. 13, 1903 805,092 Prince Nov. 21,1905

1,134,236 Shreeve Apr. 6, 1915 1,439,117 Newman Dec. 19, 1922 2,014,427 Eaton Sept. 17, 1935 2,042,821 Bennett June 2,l 1936 2,168,569 Jacoby Aug. 8, 1939 2,404,772 Brodie July 30, 1946 FOREIGN PATENTS Number Country Date 494,293 Great Britain Oct. 19, 1938 513,160 Great Britain Oct. 5, 1939 

